Interaction between inorganic sulfur compounds and heme proteins

CÓRDOVA, JONATHAN ALEXIS; PALERMO, JUAN CRUZ; ESTRIN, DARÍO ARIEL; BARI, SARA ELIZABETH; CAPECE, LUCIANA

Córdoba Capital

Congreso; LI Reunión Anual de la Sociedad Argentina de Biofisica; 2023

Sociedad Argentina de Biofisica

Heme proteins are known for the wide variety of biological activities in which they areinvolved in living organisms. In addition to their varied functions, they are receptive tosmall and endogenous signaling molecules - like CO, NO, H2S, and HSSH - that play rolesin various metabolic processes. Our main goal is to understand the migration of disulfidespecies, HSSH/HSS-, from the bulk to the active site, and their mechanism of coordinationto the metallic center. We selected two heme proteins to explore the interaction ofinorganic sulfur species with the ferric heme iron, to discriminate the role of the distalcavity in the coordination mechanism. On one hand, we use metmyoglobin (Mb) known asthe ´hydrogen atom´ of heme proteins for its extensive use in investigations of differentaspects of heme protein behavior. On the other hand, we selected the microperoxidase 11(MP11), a heme peptide derived from the proteolysis of cytochrome c as a model devoid ofdistal interactions. Interestingly, while the association constant of these species reduceswith pH in the case of Mb, it presents the opposite trend for MP11. In this work, we used acombination of experimental and computational methods to understand how the initialstage of the interaction between HSSH/HSS- (p Ka = 5.1) and MP11 happens. Themigration and binding constant (kon) of HSSH/HSS- in Mb has been recently reported bythe group at different pHs, and we present herein the estimation of the kon of HSSH/HSSat pH.6,8 by stopped-flow conditions. Additionally, using different computationalmethods such as steered molecular dynamics (sMD) and hybrid quantum mechanics/molecular mechanics calculations (QM/MM). The free energy profile of migration of HSSH/HSS- within MP11 was determined using sMD and showed similar behavior to thereported by members of our group for H2S/HS- over the same heme protein model.Additionally, the coordination reaction of HSSH/HSS- and H2S/HS- to the heme inside themodel studied was recently determined using QM/MM. Taking advantage of the dataobtained for Mb, we made a comparison of the binding process between MP11 and Mb. Inconclusion, the results in this work show that both migration towards the active site andcoordination to the heme iron are two key steps in the association process, and we providea molecular explanation for the observed trends for the variation of the associationconstant when varying the pH.